1. Field of the Invention
The present invention relates in general to the field of automotive electrical systems. Specifically, the present invention is directed to a starting apparatus of an internal combustion engine including a starter/alternator assembly and a method for controlling transition of the starter/alternator assembly from a starting mode to a generation mode by monitoring a rotational speed of the engine.
2. Description of the Prior Art
A recent trend in automotive electrical systems is the combining of the formerly separately functioning and operating starter and alternator/generator components. As automobiles become more electronics intensive, in terms of electronic accessories and sophistication of control systems, the need becomes greater for increased electrical supply. As a result, the alternator has become physically larger and more powerful as automotive electrical needs have increased.
In addition, the need for increasing operating efficiencies from internal combustion (I.C.) engines mandates a powerful and frequently operated starter motor to resume I.C. engine operation on short demand cycles. And, while these separate trends have been in place, a third element always present in automotive design is packaging efficiency in terms of underhood space. As these trends have progressed, a commonly proposed strategy is to combine the starter and alternator/generator into a single underhood starter/alternator assembly. During initial startup of the vehicle, the starter/alternator assembly functions as a starter. While functioning as a starter, the starter/alternator assembly provides a sufficient amount of torque to rotate the crankshaft of the engine before the cylinders are fired. After the engine is started, the starter/alternator assembly is used as a generator to provide electric power to the electrical system of the vehicle.
In this regard, the starter function of the starter/alternator assembly can be quite powerful vis-à-vis the I.C. engine being started inasmuch as the I.C. engine is required to achieve self-sustaining operation within ½ to 1 second of starter initiation and require significant demand of the battery. Furthermore, because of the increased demand of vehicle electrical systems, the capacity of the alternator is large and may generate substantial current during generation mode. The generator function of the starter/alternator assembly can be equally powerful vis-à-vis the capacity of the I.C. engine to generate sufficient torque especially during instances of high relative load and low relative engine speed.
In the above-described engine starting or cranking operation, it is desired to crank the engine with as large torque as possible to speedily start the engine by overcoming its large load resistance including static friction at the time of initial period of engine starting.
In the last period of engine starting after the engine is started to rotate, the engine starts to produce a driving torque and frictions at various friction surfaces in the engine changes from the static one to the dynamic one to reduce the load resistance. As a result, the rotational speed of the engine increases rapidly and large vibrations and noises are generated, thus degrading quietness and durability of the engine. Further, applying a large torque from the starter/alternator assembly to the engine to rapidly increase its rotational speed after the starting of engine rotation causes unnecessary consumption of electric power in a vehicle-mounted storage battery.